1. Field of the Invention
This invention relates to aerial refueling of a receiver aircraft having a probe for receiving fuel from a tanker aircraft having a hose and drogue system.
2. Prior Art
Aerial refueling of a receiver aircraft from a tanker aircraft has become a fairly common event. One such event was depicted in the motion picture xe2x80x9cAir Force One.xe2x80x9d Nevertheless, aerial refueling is still a difficult and dangerous operation and is typically attempted only by military pilots in military aircraft.
Today, two types of aerial refueling systems are used by the various militaries throughout the world. One is an extendible boom system and the other is a hose and drogue system. The invention relates to the latter type system.
In a hose and drogue system, the drogue is attached to the outlet end of a hoses The inlet end of the hose is attached to a reel onto which the hose is wound. The reel is typically mounted either within the tanker aircraft""s fuselage or on a refueling pod or module which is attached to the bottom of the tanker aircraft""s fuselage. When the hose is deployed, the outlet end of the hose, with its attached drogue, extends behind the tanker aircraft. Depending upon the combinations of tanker and receiver aircraft and the specifications of the particular refueling system used, the total length of the hose may be 50 feet or more, and the drogue is in a preferred refueling range when it is extending about 30 feet from the reel.
When the hose and drogue are in the fully extended position (with several turns of hose still remaining on the reel), the pilot of the aircraft to be refueled maneuvers his or her aircraft into a position such that the refueling probe of the receiver aircraft enters into and engages with the drogue. The pilot continues to urge the receiver aircraft forward relative to the tanker aircraft until the drogue is in the refueling range. As the receiver aircraft is moving forward, the hose is retracted onto the reel to take up the slack in the hose. A refueling range marker is disposed on a predetermined portion of the hose. When the pilot of the receiver aircraft sees the refueling range marker reenter the tanker aircraft""s fuselage or refueling pod, the receiver aircraft""s pilot knows that the drogue, engaged with the receiver aircraft""s probe, is in the refueling range. When the engaged drogue and probe are in the refueling range, fuel is pumped from the tanker aircraft to the receiver aircraft. After refueling is completed, the pilot of the receiver aircraft reduces its speed relative to the tanker aircraft. The hose and drogue are pulled back with the probe of the receiver aircraft, with the hose again being unwound from the reel, until the drogue and hose reach the fully extended position. At this point rotation of the reel stops, the drogue and hose cannot be pulled further back, and the receiver aircraft""s refueling probe disengages from the drogue. Retraction of the hose back onto the reel then begins.
Danger arises during the initial engagement from the fact that both the tanker and receiver aircraft are not in locked relationship with each other and the hose (at least at its outlet end) and drogue, once deployed from the tanker aircraft, are not in locked relationship with either aircraft until the refueling probe makes engagement with the drogue. With each of the aircraft traveling at hundreds of miles per hour with respect to the surrounding air, there are a significant number of mis-engagements caused by excessive closing speed between the tanker and receiver aircraft. The frequency of mis-engagements increases with darkness of evening and night. Because the drogue is being, hit with considerable force and is being displaced back toward the tanker aircraft before the pilot of the receiver aircraft can reduce the speed of the receiver aircraft to match that of the tanker aircraft, a large amount of slack is formed in the hose and the hose bends into a shape resembling a sine wave.
In this condition, the hose often goes into oscillation with the result that the drogue, xe2x80x9cwhippingxe2x80x9d about, may detach the probe from the receiver aircraft, and the drogue, either itself or with the detached probe, may hit the receiver aircraft causingloss of life and/or of the receiver aircraft.
To aid the pilots of the tanker and receiver aircraft to determine whether the drogue is in the appropriate position relative to the receiver aircraft""s refueling probe for the receiver aircraft to make its run at the drogue, it has been proposed that a device including a position sensor, a receiver and/or a transmitter (hereinafter referred to as a xe2x80x9cpositerxe2x80x9d) be mounted on each of the drogue and the probe. These positers would indicate to the pilots (particularly the receiver aircraft""s pilot) the positions of the drogue and probe with respect to each other. The receiver aircraft""s pilot would adjust the speed and position of the receiver aircraft until confirmation is received that the drogue is directly in front of the probe and the desired distance from it. With such positers, the receiver aircraft""s pilot would be receiving automated confirmation of what that pilot would ordinarily perceive visually.
In addition, it has been proposed that the drogue be fitted with jets which, in response to the relative positions of the drogue and probe, would be operated so as to maneuver the drogue up or down, left or right, or a combination of these directions, until the drogue is aligned with the probe. With such jets, the drogue could be aligned the probe even without any maneuvering of the receiver aircraft.
Both of these proposals (i.e., providing positers on the drogue and probe and fitting the drogue with jets) are intended to make alignment of the probe with the drogue quicker, easier and more reliable. They are also intended to make possible the refueling of unmanned air vehicles (commonly referred to as xe2x80x9cUAVsxe2x80x9d). In any event, the refueling process, once the drogue and probe are in alignment with each other, would remain the same. That is, the receiver aircraft initiates its run at the drogue by speeding up relative to the tanker aircraft, attempting to engage the drogue, and if successful, pushing it forward (i.e., toward the tanker aircraft) until the drogue is in the refueling range.
These proposals, either alone or in combination with each other, will not reduce the oscillation problem described above. So, notwithstanding these improvements, substantial danger would still exist in the course of engaging a drogue and hose for aerial refueling.
One method of minimizing the oscillation problem is to retract the hose quickly upon engagement (or contact) of the probe and drogue as described in the inventor""s co-pending U.S. application Ser. No. 09/643,804, now U.S. Pat. No. 6,454,212 the contents of which are hereby incorporated herein.
Alternatively, the inventor has devised a method for substantially avoiding the oscillation problem, as described hereunder.
The invention is a new method for achieving engagement of the drogue and probe for aerial refueling. Instead of having the receiver aircraft make a run at the drogue, pursuant to the invented method the tanker aircraft and receiver aircraft approximately match speed and direction, with the probe of the receiver aircraft maintained at a first predetermined distance behind the tanker aircraft until engagement of the drogue and probe is accomplished. The hose and drogue are extended rearward from the tanker aircraft so that the drogue is positioned at a second predetermined distance behind the tanker aircraft (which second predetermined distance is shorter than the first predetermined distance), the drogue and probe are orthogonally aligned with each other, and the hose is extended back beyond the second predetermined distance so that the drogue moves rearward away from the tanker aircraft to and into engagement with the probe. The force of the air stream on the drogue is sufficient to provide for secure engagement of the drogue with the probe. Once engagement is accomplished, the hose extension is stopped.
The invention may be used with almost any hose and drogue refueling system.